A wide variety of writing instruments has so far been known, and in general, the role of an ink-storing vessel of a free ink type instrument having a collector structure and a sliver type instrument and an ink-storing tube (an ink tube and a refill) of a ballpoint pen has had a principal object of storing an ink for a writing instrument such as a water-based or oil-based liquid ink and a gel ink and preventing a solvent constituting the ink from volatilizing.
Usually, these ink-storing vessel and ink-storing tube for a writing instrument are constituted of organic high molecular compounds (synthetic resins and the like) such as polypropylene from the viewpoints of the chemical stability, the solvent resistance, the economical efficiency and the productivity.
However, according to the researches and the knowledges of the present inventors, in observing with the passage of time, air, especially oxygen penetrates into an ink-storing vessel or an ink-storing tube, whereby the ink is oxidized, and accelerated are the problems of deterioration in the ink itself such as thickening of the ink and reduction in a density of the colorant, reduction in the writing property due to solidification in the ink caused by generation of bubbles and due to clogging in the ink-feeding passage and leaking of the ink due to a rise in the internal pressure, and involved therein is the problem of reducing a performance and a quality of the writing instrument and shortening the life thereof.
In the case where an ink for a writing instrument is a water-based ink, water, which is a principal solvent for the ink, vaporizes and penetrates through an ink-storing member, which results in losing the amount, to thereby bring about deterioration in the ink such as solidification in the ink, coagulation of the colorant and a rise in the viscosity, and involved therein are the problems of reduction in the quality of the writing instrument such as reduction in the writing property and a fall in the writing distance and shortening the life.
Also, in the case where an ink for a writing instrument is an oil-based ink, steam (humidity) present in the air penetrates through an ink-storing member and gets into the ink, whereby deterioration in the ink such as a rise in the viscosity caused by deposition of the resin and the colorant is caused, and the problem of reducing the writing quality and shortening the life is involved therein.
Further, when polypropylene, which is inexpensive and excellent in moldability and transparency, is used for an ink-storing member in a pressure type ballpoint pen, involved therein is the problem that a pressurized gas such as nitrogen gas present in the ink-storing vessel or the ink-storing tube penetrates to the outside of the vessel or the tube to cause reduction in an internal pressure of the vessel or the tube, whereby inferior writing is brought about.
On the other hand, known as a conventional ink-storing member for a writing instrument are, for example, a ballpoint pen refill in which a ballpoint pen tip rotatably holding a ball is mounted directly or via a tip holder at a point of a resin-made ink-storing tube directly filled with an ink for a ballpoint pen, wherein the periphery of the ink-storing tube described above is covered with a metal member such as stainless steel and bronze in order to prevent the ink from leaking from the interfitting parts of the ink-storing tube and the ballpoint pen tip, the tip holder or the plug and obtain a high grade appearance (Japanese Patent Application Laid-Open No. 11989/2002), and a resin-molded vessel for storing an ink for a writing instrument characterized by comprising a multilayer structure in which two or more resin layers are formed and at least one layer of the resin layers is formed with an ethylene-vinyl alcohol copolymer resin (EVOH) in order to prevent volatilization of a solvent and/or vaporization of moisture contained in the ink for a writing instrument (Japanese Patent Application Laid-Open No. 307890/2002).
On the other hand, in respect to a method for preventing discoloration in a writing instrument, known as a packaging method for an antibacterial agent-containing writing instrument is, for example, a packaging method for antibacterial agent-containing stationeries which can prevent the stationeries from being discolored by allowing a deoxidizing agent to be present in the packaging material to inhibit the stationeries from being brought into contact with oxygen and moisture present in the air to the utmost (Japanese Patent Application Laid-Open No. 133346/1996).
However, in the ballpoint pen refill described in Japanese Patent Application Laid-Open No. 11989/2002, the periphery of the ink-storing tube is merely covered with a metal member, and therefore the refill is inferior in visibility for the ink contained therein and provides the problem that it is difficult to observe the ink remaining amount. Further, the problem that a sticking work of the resin and the metal member is complicated is brought about.
Also, the resin-molded vessel for storing an ink for a writing instrument having a multilayer structure described in Japanese Patent Application Laid-Open No. 307890/2002 has a film-like EVOH layer of 10 to 150 μm thick, but it has the problem that it is still inferior in a gas-barrier property and a writing quality and has the problem of leaking of the ink.
Further, in the technique described in Japanese Patent Application Laid-Open No. 133346/1996, stationeries such as antibacterial agent-containing writing instruments are prevented from being discolored by oxidation when left standing for displaying in a showcase in a shop over a long period of time (from after production up to passing into the consumers), and the present invention is different from the application in an object, action and constitution (technical concept).
Further, a technique in which components such as polyphenol, vitamin C, vitamin E and others reacting with or absorbing oxygen which are antioxidants is added to an ink is also known as a method for preventing oxidation of the ink caused by air (oxygen) mixed in the ink, which is introduced thereinto in preparing and filling the ink.
In these techniques, however, the addition amounts are naturally restricted to be very small amounts, and therefore the problem that the function thereof is lost in a relatively short period is involved therein. The problems of oxidative deterioration in an ink caused by penetration of oxygen through an ink-storing member and deterioration due to vaporization or absorption of moisture caused by permeation of steam are not recognized in the techniques described above.
In light of the problems and the existing situations in the conventional techniques described above, the present invention intends to solve them, and an object thereof is to provide an ink-storing member for a writing instrument such as an ink-storing vessel or an ink-storing tube for a writing instrument which stores an ink for a writing instrument such as a water-based or oil-based liquid ink and a gel ink, wherein solved are prevention of deterioration in the ink caused by permeation of oxygen and nitrogen in the air, inhibition in leaking of the ink and generation of bubbles, a rise in the ink-discharge stability, improvement in fragrance retention in a perfume-containing ink and inferior writing brought about by reduction in an internal pressure in the vessel caused by permeation of a pressurized gas in an ink-storing vessel into the outside in a pressure type writing instrument such as a pressure type ballpoint pen pressurized by gas such as nitrogen gas; the visibility is excellent; and the remaining amount of the ink can readily be observed.
Further, an object of the present invention is to provide an ink-storing member for a writing instrument which can solve the problems of reduction in the performance quality and the life brought about by reduction in the amount of water, which is a principal solvent, caused by permeation through the ink-storing member after being turned into steam in the case of using a water-based ink and the problems of reduction in the performance and the life brought about by moisture in the air which permeates through the ink-storing member and gets into the ink in the case of using an oil-based ink.